Stephanie is 5 times as old as William and is also 28 years older than William. How old is William?
Answer: We can use the given information to write down two equations that describe the ages of Stephanie and William. Let Stephanie's current age be $s$ and William's current age be $w$ $s = 5w$ $s = w + 28$ Now we have two independent equations, and we can solve for our two unknowns. Since we are looking for $w$ , and both of our equations have $s$ alone on one side, this is a convenient time to use elimination. Subtracting the second equation from the first equation, we get: $0 =$ $5w$ $-$ $ (w + 28)$ which combines the information about $w$ from both of our original equations. Solving for $w$ , we get: $4 w = 28$ $w = 7$.